The visual structure of galaxies, their morphologies, reveal a lot of information about the ongoing physical processes in galaxies. Galaxies interact gravitationally with each other, so the effects of the environment can be studied via galaxy structure. Galaxy structure can be studied by fitting analytical light profile functions to the observed images. The fitting is based on an assumption that the shape of the galaxy can be described by certain analytical forms. This kind of parametric studies can be done using the GALFIT software. As a result, these fitted models give values for the fundamental parameters describing galaxy size, shape and brightness.
In this Master's thesis I introduce GALFIT as a tool for structural studies and morphological classifications of galaxies. I have gathered a sample of group member spiral galaxies in multiwavelength Hubble Space Telescope CANDELS survey data. I have completed detailed multicomponent and multiwavelength fits for 9 galaxies from the sample of 73 galaxies. The results are used to study stellar mass-to-light ratios and star formation using galaxy colors. Also a variety of asymmetry measurements are calculated for a subsample of these 9 galaxies. The results imply that the fitting process should be unified to measure similar comparable parameters for the entire sample.
I have used my knowledge in GALFIT in a study of galaxies in the infalling groups observed in LoCuSS survey by completing bulge-to-disk decomposition fitting for a sample of several hundred galaxies. The sample galaxies are classified based on the Sérsic indices from my fits and tests verify the classification. The results imply that the effect of mass-quenching is negligible in the infalling galaxy groups. The results also imply that the star-forming galaxies are more elongated than the passive ones, and that the bulge luminosity of the star-forming galaxies rise towards the center of the cluster, however with a low statistical significance.
GALFIT is capable of producing images based on the initial input parameter values if it's not used to fit existing data. I have applied this feature to simulate mock observational data of fields covered in galaxies for the Euclid mission. The images accompanied with catalogs of coordinates, magnitudes and position angles of the objects are used by the Euclid group in Helsinki as independent test data for developing validation tools for Euclid data simulations.